Conventionally, in an optical module equipped with an optical modulator for modulating light, an input optical fiber and an output optical fiber are respectively connected in series on both sides of the optical modulator. However, when the input optical fiber and the output optical fiber are respectively connected to both sides of the optical modulator, the mounting area of the optical modulator is increased.
Therefore, in the optical module, connecting, to one side of the optical modulator, the input optical fiber and the output optical fiber disposed in parallel sometimes reduces the mounting area.
In the optical module that connects, to one side of the optical modulator, the input optical fiber and the output optical fiber disposed in parallel, the direction of light is changed between an end portion of the input optical fiber and an end portion of the output optical fiber. That is, for example, a bent portion is provided in an optical waveguide on an optical modulator chip, and the bent portion of the optical waveguide folds back light between the end portion of the input optical fiber and the end portion of the output optical fiber. At this time, a radio frequency (RF) electrode for high-frequency signal for modulating light is disposed closer to the end portion of the input optical fiber than the bent portion along the optical waveguide. On the other hand, a direct current (DC) electrode for a direct current signal (bias voltage) for adjusting the phase of light is disposed closer to the end portion of the optical fiber on the output side than the bent portion along the optical waveguide. Then, an RF signal is input to an RF electrode from an RF terminal provided on a side surface of a package or the like. Similarly, the bias voltage is input to a DC electrode from a DC terminal provided on the side surface of the package or the like.
Patent Literature: JP 2012-163876 A
Incidentally, in an optical module, a reception interface (hereinafter abbreviated as “reception IF”) for externally receiving an RF signal used for modulating light in an optical modulator is often disposed at a position opposite to the end portion of the output optical fiber with the optical modulator interposed therebetween. Therefore, when light is folded back between the end portion of the input optical fiber and the end portion of the output optical fiber by a bent portion of the optical waveguide on the optical modulator chip, the RF electrode disposed on the end portion side of the input optical fiber may be formed at a position away from the reception IF of the RF signal. At this time, since it is difficult to separate the RF terminal for inputting an RF signal to the RF electrode from the RF electrode, the RF terminal and the RF terminal may be provided at a position away from the reception IF of an RF signal.
However, the longer the RF terminal is away from the reception IF of a RF signal, the longer the wiring connecting the RF terminal and the reception IF of an RF signal becomes. Therefore, in a case where light is folded back between the end portion of the input optical fiber and the end portion of the output optical fiber by the bent portion of the optical waveguide on the optical modulator chip in order to reduce the mounting area of the optical modulator, there is a problem that the propagation loss of an RF signal used for modulating light increases.